i sleep however is comfortable... from what i hear it's ok to do so this early in the game. i usually fall asleep on my stomach and wake up on my back for some reason.
as of late, laying on my right side (which is how i normally fall asleep) is not so good. it seems early on for it to bother me, but it does in a slight, annoying tug-y cramp-y kinda way, so i avoid it generally...